1. Field of the Invention
The present invention relates to a compression ratio changing device in an internal combustion engine for changing the compression ratio between two stages, i.e., low and high stages in which a connecting rod connected at its smaller end to a piston is carried at its large end on a crank pin of a crank-shaft, and particularly, to an improvement in a compression ratio changing device of a type including an eccentric ring which is interposed between the crank pin and the large end of the connecting rod and whose inner and outer peripheral surfaces are eccentric from each other.
2. Description of the Prior Art
Such type of the compression ratio changing device is already known, as disclosed, for example, in Japanese Patent Application Laid-open No. 121837/87.
The following devices are disclosed in the Japanese Patent Application Laid-open No. 121837/87: (1) a device in which the eccentric ring is connected to the large end of the connecting rod, so that the eccentric direction of the eccentric ring can be switched between opposite directions, and (2) a device in which the eccentric ring is connected to the crank pin, so that the eccentric direction of the eccentric ring can be switched between opposite directions. In the device (1), the stroke of the piston is not changed, but the position of top and bottom dead centers of the piston are only changed, by switching the eccentric direction of the eccentric ring, and therefore, the compression ratio is changed only to a small extent. In the device (2), the stroke of the piston is increased or decreased by switching the eccentric direction of the eccentric ring, but in a high compression ratio state with an increased stroke of the piston, the position of the bottom dead center of the piston is lowered and for this reason, the compression ratio cannot be sufficiently increased. Therefore, in either of the devices (1) and (2), if a large change in compression ratio is desired, an eccentric ring having a large eccentric amount is required and hence, an increase in size of the engine is imposed.